The invention relates to a two-layer system which can be cured by radiation and to the use thereof for the production of polymeric coatings.
Radiation-curable systems are materials which are sought after and are frequently employed in the production of photopolymerized coatings for surface finishing and in the production by photolithography of photopolymerized relief structures. The main field of use in this respect is the production of paint coatings on a very wide variety of substrates. In addition, such materials are used, in the production of microelectronic and optoelectronic components and switch gear, as a photoresist in the production of switching structures or in the latter as protective or passivating layers having special resistance to heat and chemicals, as insulating layers or as dielectrics or, in liquid-crystal display cells, as orientation layers. Further applications are use as an etch resist and plating resist and as a solder resist in the production of printed circuits and printing plates and other reprographic materials. Finally, systems of this type are also suitable for the preparation of anisotropic polymer coatings for use in the field of non-linear optics.
The multifarious methods of preparing radiation-curable systems can be inferred, for example, from W. S. De Forest: Photoresist Materials and Processes, McGraw-Hill, New York, 1975, and also German Patent Specifications 2,380,830, 2,437,348 and 2,722,264 and European Patent Specification 3,002.
The processes and methods hitherto known exhibit a number of disadvantages. Thus their sensitivity is frequently unsatisfactory, as a result of which exposure times of several minutes are required, using the customary radiation sources, for adequate photo-crosslinking and the layer hardness caused thereby and for ensuring the resolution and edge steepness in relief structures which are necessary in microelectronics. Secondly, inadequate resolving power and unsatisfactory edge steepness, caused, for example, by under-irradiation of the copying layer or by reflections at the substrate, are a source of criticism of the known photopolymerizable systems.
A further problem in coatings of all kinds is the adhesion of the film to the substrate. Detachment of the coating from the substrate occurs frequently, particularly in the case of substrates of an irregular shape or materials subjected to considerable bending stresses.
Finally, there is often a need for coatings which have a homogeneous thickness within a wide area, which in most cases can only be achieved with dificulty by means of conventional coating techniques.